Herein disclosed is a semiconductor integrated circuit device fabricating
process for forming MISFETs over the principal surface in those active regions
of a substrate, which are surrounded by inactive regions formed of an element separating
insulating film and channel stopper regions, comprising: the step of for forming
a first mask by a non-oxidizable mask and an etching mask sequentially over the
principal surface of the active regions of the substrate; the step of forming a
second mask on and in self-alignment with the side walls of the first mask by a
non-oxidizable mask thinner than the non-oxidizable mask of the first mask and
an etching mask respectively; the step of etching the principal surface of the
inactive regions of the substrate by using the first mask and the second mask;
the step of forming the element separating insulating film over the principal surface
of the inactive regions of the substrate by an oxidization using the first mask
and the second mask; and the step of forming the channel stopper regions over the
principal surface portions below the element separating insulating film of the
substrate by introducing an impurity into all the surface portions including the
active regions and the inactive regions of the substrate after the first mask and
the second mask have been removed.
